Reminds me of something that happened some 300 years ago: European explorers noticed that the African tribes of a certain locale had this superstition against stepping in puddles when it rained. The explorers, hoping to “teach [the natives] a lesson in superstition”, decided to jump in the puddles barefooted.

When they went back home they were all ridden with a strange worm parasite that is only found in that part of the world.